User Notes:

In the example for send_message.php It doesn't delete the message from the queue. With the example it would keep sending the queued messages over and over again. I had to add change the sendMail function in Queue.php
from this
if (!PEAR::isError($sent) && $sent && $set_as_sent) {
$this->container->setAsSent($mail);
}

the mime encoding of the attachments plus message and ancillary data stored in the mailbody may push the size of required storage of that which might be used for the raw data that you may be storing elsewhere in the database.

in other words - always make sure the fields in your database are
[more than] large enough for the data going in: if you are storing raw data in a blob and mail_queue is not delivering the constructed mails properly, perhaps you should use a longblob as the datatype for the body field in the mail_queue table.